The invention pertains to methods of forming field emission emitter tips.
Field emitters are widely used in display devices, such as, for example, flat panel displays. Clarity, or resolution, of a field emission display is a function of a number of factors, including emitter tip sharpness. Specifically, sharper emitter tips can produce higher resolution displays than less sharp emitter tips. Accordingly, numerous methods have been proposed for fabrication of very sharp emitter tips (i.e., emitter tips having tip radii of 100 nanometers or less). Fabrication of very sharp tips has, however, proved difficult. It has proved particularly difficult to build large areas of sharp emitter tips using photolithography while maintaining resolution and stringent dimensional control over large area substrates used for display manufacture. In light of these difficulties, it would be desirable to develop alternative methods of forming emitter tips. Several methods have been proposed. Some utilize deposited particles to form a non-photolithographic etch mask. A subsequent etching step or series of steps forms the emitter tips. The use of deposited particles on a substrate as an etch mask can reduce complexity of an etching process and improve sharpness of emitter tips relative to photolithographic processing. A difficulty with present methods of using deposited materials as an etch mask is that the materials are frequently non-uniformly deposited on a substrate surface. Accordingly, emitter tips patterned from the deposited materials are not uniformly formed across a substrate surface. It would be desirable to develop alternative methods of using deposited materials as masking layers in emitter tip formation wherein the deposited materials are uniformly deposited across a substrate surface to enable a uniform distribution of emitter tips to be etched into the substrate surface.
In methodology understood to be unrelated and never applied to emitter tip formation, Langmuir-Blodgett processing has been developed as a technique for providing a monolayer of particulates over a substrate surface. Langmuir-Blodgett processing in the context of this application involves submerging a substrate in a liquid and providing particulates floating on a surface of the liquid. The particulates are preferably in the form of a monolayer on the liquid surface. The monolayer can be maintained as a tightly packed monolayer by providing a pushing bar to compact the particulates together. The substrate is subsequently pulled through the tightly packed monolayer to form an even coating of particulate materials on the substrate surface.
In one aspect, the invention encompasses a method of forming field emission emitter tips. A masking material is provided over a semiconductor substrate to form a masking-material-covered substrate. At least a portion of the masking-material-covered semiconductor substrate is submerged in a liquid. Particulates are provided to be suspended on an upper surface of the liquid. While the particulates are suspended, the submerged masking-material-covered substrate is moved relative to the suspended particulates to form a layer of the particulates supported on the masking material of the masking-material-covered substrate. In a subsequent step, a dimension of the particulates is decreased to leave some portions of the masking material covered by the particulates and other portions of the masking material uncovered by the particulates. After decreasing the dimension and while the particulates are supported on the upper surface, the masking-material-covered substrate is exposed to first etching conditions to remove uncovered portions of the masking material while leaving covered portions of the masking material over the substrate to define a patterned masking layer. The particulates can then be removed. While the so patterned masking layer is over the semiconductor substrate, the semiconductor substrate is exposed to second etching conditions to pattern the semiconductor substrate into emitter tips.